1. Field of the Disclosure
The present invention relates generally to power converters, and more specifically, the invention relates to control circuits that detect a peak input voltage.
2. Background
Many electrical devices such as cell phones, personal digital assistants (PDA's), laptops, etc. are powered by a source of DC power. Because power is generally delivered through a wall outlet as high-voltage AC power, a device, typically referred to as a power converter, is required to transform the high-voltage AC power to usable DC power for many electrical devices. The usable DC power may be provided by the power converter directly to the device or it may be used to charge a rechargeable battery that, in turn, provides energy to the device, but which requires charging once stored energy is drained. In operation, a power converter may use a controller to regulate output power delivered to an electrical device that may be generally referred to as a load. The controller regulates the transfer of energy to the load. In one instance a controller may control a power switch to turn on and off in response to feedback information from a sensor to transfer energy pulses to the output from the high-voltage AC power source.
The high-voltage AC power source typically includes a cyclic input voltage signal. For example, the usual waveform of an AC power source is that of a sine wave. The peak value of each cycle of the input voltage signal may be used for a variety of purposes, including to control the switching of the power switch. However, the peaks of the input voltage signal may vary with time. That is, the peak input voltage may increase or decrease from cycle to cycle.